Handoff method in fmipv6 for seamless tcp packet transmissions

ABSTRACT

A handoff apparatus and method in FMIPv6 for seamless TCP packet transmissions. The handoff method includes steps of intercepting by a previous access router certain TCP packets sent from a correspondent node to a previous temporary address of a mobile node; and creating a TCP ACK by the previous access router in response to the certain TCP packets and sending by the previous access router the created TCP ACK to the correspondent node every time the certain TCP packets are forwarded to a new access router through a bi-directional tunnel. The handoff method has an advantage in that the packet transmission rate can be secured at the same level as the mobile node stays still during the performance of the handoff of the mobile node since the previous access router instead of the mobile node creates and sends the TCP ACK to the correspondent node during the performance of the handoff of the mobile node.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/324,302, which claims priority from Korean Patent Application10-2005-0010747 filed on Feb. 4, 2005, the disclosures of which areincorporated herein in their entireties by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Methods and apparatuses consistent with the present invention relate toa handoff for mobile nodes, and more particularly to a handoff in FMIPv6for seamless TCP packet transmissions.

2. Description of the Related Art

Recently, more people use wireless internet due to the rapid spread ofthe internet, advancement of wireless communication technologies, andimproved performance of mobile terminals such as portable computers,Personal Digital Assistants (PDAs), etc. Under such wireless internetenvironments, the mobile terminals change their points for connectionsto networks frequently as they roam around. Such mobile terminals arereferred to as mobile nodes.

In order to enable the mobile nodes to access the wireless internet, thehigh-quality internet service has to be served to the mobile nodes tothe same extent as in a home network even though the mobile nodes maymove to a foreign network out of their home network. Diversetechnologies have been proposed for stable wireless internet serviceseven when the mobile nodes change points for connections to networks. Inparticular, the Mobile Internet Protocol (IP) Working Group of theInternet Engineering Task force (IETF) has proposed a method for allmobile terminals to continuously use a specific identifier of IP addressregardless of network connection points, and continues to defineprotocols for mobile IPs. Further, in order to solve a problem of theexisting IP version 4 (IPv4) address system such as insufficientaddresses for meeting increasing address demands, the Mobile IPv6 isbeing introduced to provide wireless internet services using the IPv6.The mobile IP version 6 (IPv6) is revised up to IETF Internet-Draftversion 24 from the original proposal thereof, and may be turned intothe Request For Comments (RFC) sooner or later.

The mobile IPv6 creates a new Care-of Address (CoA) upon handoff, andhas inevitable delay factors such as movement detection, IP addressconfiguration, and location update, until the completion of thenewly-created address registration. The total delay caused by the delayfactors can be large enough to be avoided when real-time applications orapplications sensitive to losses are involved. As a technology forreducing such delays, the Fast Mobile IPv6 (FMIPv6) has been proposedwhich can immediately deliver data when a new link is detected as wellas deliver packets to mobile terminals immediately at the time ofconnection to a new link.

However, even in such FMIPv6 environments, if the mobile nodes are notphysically connected to any wireless access point during the handoffdelay time period, the mobile nodes can not receive Transmission ControlProtocol (TCP) packets sent from a correspondent node (CN) tocommunicate therewith, nor send an acknowledgement to the correspondentnode CN. That is, the FMIPv6 environment causes communication cutoffevents due to characteristics of the TCP during TCP-based communicationsof the mobile nodes, as the mobile nodes roam around, two occasions ofwhich can be considered and described in detail below.

First, description will be made for the event where the handoff endsbefore the TCP retransmission timeout (RTO) is issued. In this case,during the handoff time period, the TCP window of the correspondent nodeCN does not slide since the correspondent node CN can not receive a TCPacknowledgement (ACK) from a mobile node, and, if the TCP ACK is sentthrough a new access router NAR after the mobile node completes itshandoff, the window of the correspondent node CN slides again. That is,the packet transmission rate decreases only while the window of thecorrespondent node CN stops its sliding, and, after the handoff iscompleted, the packet transmissions resume with a window size previouslyused.

Next, description will be made for the event where the TCP timeout iscaused due to a longer handoff time period during the handoffperformance. In this case, since the correspondent node CN can notreceive the TCP ACK until the TCP timeout occurs before the handoffcompletion, the window of the correspondent node CN does not slide, andreduces its size to 1 due to the TCP slow-start. If the window size isreduced as above, it takes much time to restore the window size up tothe previous window size even when the TCP ACK is sent to thecorrespondent node CN through the new access router, after the mobilenode completes the handoff. Further, since the correspondent node CN cansend only as many packets as corresponds to the window size and due tothe limitation for the number of packets that can be sent until thewindow size of the correspondent node CN is restored up to the previouswindow size, the packet transmission rate becomes lower.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide a handoff method inFMIPv6 for seamless TCP communications and improved TCP packettransmission rate by preventing communication cutoff events due to thecharacteristics of the TCP protocol during the handoff of a mobile node.

According to an aspect of the present invention, there is provided ahandoff apparatus and a handoff method in FMIPv6 for seamless TCP packettransmissions, comprising steps of intercepting by a previous accessrouter certain TCP packets sent from a correspondent node to a previoustemporary address of a mobile node; and creating a TCP ACK by theprevious access router in response to the certain TCP packets andsending by the previous access router the created TCP ACK to thecorrespondent node every time the certain TCP packets are forwarded to anew access router through a bi-directional tunnel.

In an exemplary embodiment of the present invention, TCP connections arepreferably formed between the correspondent node and the previous accessrouter.

In an exemplary embodiment of the present invention, TCP connections areformed between the previous access router and the mobile node.

In an exemplary embodiment of the present invention, if the TCP ACK isreceived from the previous access router, the correspondent nodecontinues to send next TCP packets to the previous access router.

In an exemplary embodiment of the present invention, the previous accessrouter stores TCP packets received from the correspondent node and sendsthe TCP packets to the mobile node after sending the corresponding TCPACK to the correspondent node, and secures the delivery of TCP packetsto the mobile node by re-transmitting the stored TCP packets when thepacket was lost during delivery.

BRIEF DESCRIPTION OF THE DRAWINGS

The above aspects of the present invention will be more apparent bydescribing exemplary embodiments of the present invention with referenceto the accompanying drawings, in which:

FIG. 1 is a view showing a basic FMIPv6 structure for performing anexemplary embodiment of the present invention; and

FIG. 2 is a flow chart explaining a handoff method in FMIPv6 forseamless TCP packet transmissions according to an exemplary embodimentof the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a view for showing a basic FMIPv6 structure for performing anexemplary embodiment of the present invention. In FIG. 1, a referencenumeral 20 denotes a previous access router (PAR), reference numeral 30denotes a new access router (NAR), reference numeral 40 denotes a mobilenode (MN), and reference numeral 10 denotes a correspondent node (CN) 10communicating with the mobile node 40.

If the mobile node 40 moves to the new access router 30 from theprevious access router 20, it is assumed that the mobile node 40 or theprevious access router 20 can obtain two-layer information of the newaccess router 30 in advance before two-tier handoff is completed. If themobile node 40 obtains the two-layer information of the new accessrouter 30, the mobile node 40 requests the previous access router 20 forIP-layer information on the new access router 30.

The previous access router 20 uses the existing information on the newaccess router 30 to configure in advance a New CoA (NCoA) that will beused for the new access router 30, and notifies the mobile node 40 ofthe NCoA, so as to enable the mobile node 40 to perform a binding updateimmediately when linked to a new network. Further, the previous accessrouter 20 sets up a bi-directional tunnel with the new access router 30and tunnels packets to the new access router 30 in order to prevent lossof packets sent from the correspondent node 10 before the binding updateis completed for the NCoA.

The previous access router 20 according to an exemplary embodiment ofthe present invention includes a TCP ACK generation module. That is, assoon as packets are tunneled to the new access router 30 through a setbi-directional tunnel, the previous access router 20 generates and sendsa TCP ACK to the correspondent node 10. If the correspondent node 10receives the TCP ACK, the window of the correspondent node 10 slides. Ifthe window of the correspondent node 10 slides as above, thecorrespondent node 10 can send next TCP packets seamlessly.

FIG. 2 is a flow chart explaining a handoff method in FMIPv6 forseamless TCP packet transmissions according to an exemplary embodimentof the present invention. In FIG. 1 and FIG. 2, if the mobile node 40detects its movement to the new access router 30, the mobile node 40sends to the previous access router 20 a Router Solicitation for ProxyAdvertisement (RtSolPR) message requesting for information on the newaccess router 30 (S210). In this case, the RtSolPR message contains alink-layer identifier (ID) with respect to the new access router 30. Ifa wireless local area network (LAN) is used, the link-layer ID can bethe (B)SSID of the new access router 30.

The previous access router 20 receiving the RtSolPR message uses theexisting information on the new access router 30 to configure a newtemporary address NCoA, and sends the NCoA to the mobile node 40 in theform of a Proxy Router Advertisement (PrRtAdv) message (S220). Here, itis assumed that the previous access router 20 and the new access router30 can communicate with each other and share the information on eachother. If the previous access router 20, rather than the mobile node 40,detects the movement of the mobile node 40, the previous access router20 sends to the mobile node 40 the PrRtAdv message containinginformation on the new access router 30 without the RtSolPR message.

The mobile node 40 receiving the PrRtAdv message sends to the previousaccess router 20 the Fast Binding Update (FBU) message requesting forthe binding of the previous temporary address and the new access router30 (S230). If the previous access router 20 receives the FBU, theprevious access router 20 sends a HI message to the new access router 30to set up a bi-directional tunnel with the new access router 30 (S240).The HI message requests the new access router 30 for authentication withrespect to the newly configured temporary address NCoA.

The new access router 30 sends the HACK message in response so that thebi-directional tunnel is configured, and authenticates on the newtemporary address NCoA (S250). The previous access router 20 sends theauthentication of the new temporary address NCoA to the mobile node 40through FBACK (S260), intercepts packets sent from the correspondentnode 10 to the previous temporary address of the mobile node 40, andforwards the intercepted packets to the new access router 30 through thebi-directional tunnel (S270). At the time when the previous accessrouter 20 according to an exemplary embodiment of the present inventiontunnels the TCP packets received from the correspondent node 10 to thenew access router 30, the previous access router 20 creates and sends aTCP ACK to the correspondent node 10. If the correspondent node 10receives the TCP ACK, the window of the correspondent node 10 slides. Asabove, if the window of the correspondent node 10 slides, thecorrespondent node 10 can send next TCP packets seamlessly.

If the new access router 30 configures a new link with respect to themobile node 40, the mobile node 40 puts the Fast Neighbor Advertisement(FNA) notifying of its existence in the Router Solicitation (RS) messagefor sending (S280). Next, the new access router 30 delivers data to themobile node 40 (S290), and the mobile node 40 uses the new temporaryaddress NCoA to perform the binding update procedures coded in themobile Ipv6.

As stated above, the present invention has an advantage in that thepacket transmission rate can be secured at the same level as the mobilenode stays still during the performance of the handoff of the mobilenode since the previous access router PAR instead of the mobile node MNcreates and sends the TCP ACK to the correspondent node CN during theperformance of the handoff of the mobile node MN.

The foregoing embodiments are merely exemplary and are not to beconstrued as limiting the present invention. The present teaching can bereadily applied to other types of apparatuses. Also, the description ofthe exemplary embodiments of the present invention is intended to beillustrative, and not to limit the scope of the claims, and manyalternatives, modifications, and variations will be apparent to thoseskilled in the art.

1. A Fast Mobile Internet Protocol version 6 (FMIPv6) address systemwhich performs a handoff resulting in seamless Transmission ControlProtocol (TCP) packet transmissions, the FMIPv6 system comprising: a newaccess router; a previous access router which uses existing informationon the new access router to configure in advance a new care-of address(NCoA) used for the new access router; a mobile node which moves to thenew access router from the previous access router; and a correspondentnode communicating with the mobile node; wherein the previous accessrouter notifies the mobile node of the NCoA to enable the mobile node toperform a binding update when linked to a new network, and sets up abi-directional tunnel with the new access router and tunnels packets tothe new access router in order to prevent loss of packets sent from thecorrespondent node before the binding update is completed for the NCoA.2. The FMIPv6 system as claimed in claim 1, wherein the previous accessrouter obtains two-layer information of the new access router in advancebefore two-tier handoff is completed.
 3. The FMIPv6 system as claimed inclaim 2, wherein the mobile node obtains two-layer information of thenew access router and requests the previous access router for IP-layerinformation on the new access router.
 4. The FMIPv6 system as claimed inclaim 1, wherein the previous access router comprises a TCPacknowledgement (ACK) generation module which generates and sends a TCPACK to the correspondent node as soon as packets are tunneled to the newaccess router through the set bi-directional tunnel.
 5. The FMIPv6system as claimed in claim 4, wherein a window of the correspondent nodeslides when the correspondent node receives the TCP ACK, and next TCPpackets are sent seamlessly from the correspondent node.